1. Field of the Invention
The present invention relates to an electromagnetic coil assembly for use in an electromagnetic apparatus, such as an electromagnetic clutch for use in controlling the transmission of power from an automobile engine to a refrigerant compressor in an automobile air conditioning system. More particularly, it relates to the mounting structure for a thermal protection device, electrical wires, and caulking terminals in the electromagnetic coil assembly.
2. Description of Related Art
Referring to FIGS. 1 and 2, an electromagnetic coil assembly 4, which comprises a bobbin 1 and a coil 3, is known in the art. Bobbin 1 has a toroidal shape having a spool portion, which has an exterior open edge. Coil 3 is formed of electrical wire 2, which is wound around the spool portion. An electromagnetic coil assembly 4, for example, is used in an electromagnetic clutch 6 of a compressor 5 in an automobile air conditioning system, as shown in FIG. 3. Electromagnetic coil assembly 4 may be provided with a thermal protection device 7, e.g., a thermal fuse or a thermal switch, which is sensitive to high temperatures in electromagnetic clutch 6. Thermal protection device 7 isolates a power source, such as an automobile engine, to protect electromagnetic clutch 6 and compressor 5 when high temperatures due to friction are generated between the parts in electromagnetic clutch 6.
Referring again to FIGS. 1 and 2, thermal protection device 7 has a pair of leads, a first lead 7a and a second lead 7b, extending from either end of thermal protection device 7. An end of first lead 7a of thermal protection device 7 is connected to a wire end portion 2a of electrical wire 2 through a first caulking terminal 8. An end of second lead 7b of thermal protection device 7 is connected to a third lead 9, which is connected to the external power source (not shown), through a second caulking terminal 10. Thermal protection device 7, first lead 7a and second lead 7b, wire end portion 2a, and third lead 9 are disposed on a first end surface 1a of bobbin 1. A securing member 11 having a groove-shaped cross-section is fixed securely on first end surface 1a by adhesives. Thermal protection device 7 is fitted into the groove-shaped portion of securing member 11. A pair of projection portions 12a and 12b are formed on first end surface 1a. First lead 7a and second lead 7b are fixeded to projection portions 12a and 12b, respectively. Consequently, thermal protection device 7, as well as first caulking terminal 8 and second caulking terminal 10, is fixed to first end surface 1a of bobbin 1.
As shown in FIG. 1, electromagnetic coil assembly 4 is inserted into a core ring 13 having a groove-shaped cross-section and a toroidal shape in plan view, such that thermal protection device 7 on first end surface 1a is positioned in an open end of core ring 13. Thereafter, a resin 14 is poured into the open end of core ring 13, and electromagnetic coil assembly 4 is fixed within core ring 13.
In electromagnetic coil assembly 4, the retention strength of thermal protection device 7, first caulking terminal 8, and second caulking terminal 10 within core ring 13 is relatively low. Therefore, resin 14 may enter into the spaces between thermal protection device 7, first caulking terminal 8, and second caulking terminal 10 and first end surface 1a of bobbin 1. Consequently, thermal protection device 7, first caulking terminal 8, and second caulking terminal 10 may be pushed upward by resin 14 entering into the spaces between these elements, and as a result, these elements may not be covered by resin 14 and may be exposed outside core ring 13. Thus, when electromagnetic coil assembly 4 disposed in core ring 13 is equipped with the parts, which comprise, for example, electromagnetic clutch 6, defects or damage may occur at thermal protection device 7, first caulking terminal 8, and second caulking terminal 10.